You might be able to see that adding another 0.50 will take the total to 9.00, and multiplying by another 0.50 will take the product to 9.00.

The answer can also be found using algebra. If we call the missing price P, we have:

1.50 + 3.00 + 4.00 + P = 1.50 x 3.00 x 4.00 x P

8.50 + P = 18.00 x P

8.50 = 18.00 x P - P

8.50 = 17.00 x P

8.50 ÷ 17.00 = P

P = 0.50. QED.

Puzzle 20

Using the BrainTracker grid below, how many words can you find? Each word must contain the central Y and no letter can be used twice, however, the letters do not have to be connected. Proper nouns are not allowed, however, plurals are. Can you find the nine letter word?